1. Field of the Invention
This invention relates to electromagnetic fluid flow transducers and more specifically to extracorporeal blood flow equipment for clinical use.
2. Description of the Prior Art
Electromagnetic fluid flow systems and more particularly blood flow transducers, have been used for many years and are typically described in structure and concept in U.S. Pat. Nos. 3,487,826; 3,516,399; and 3,805,768, the contents of which are incorporated herein by reference. The principle involved in these is references is Faraday's Law, i.e., passing a fluid, for example blood, either in a tube or blood vessel, at right angles to a magnetic field to produce an electromagnetic force in a direction perpendicular to the flux lines of the magnetic field and the direction of blood flow. The blood functions as a moving conductor cutting through the magnetic field. The electromotive force (voltage) is directly proportional to the velocity of flow and volume rate of flow, the strength of the magnetic field, and the length of the conductor. Such force can be measured by diametrically opposed electrodes positioned with respect to each other to form a line perpendicular to the lines of flux established by the magnetic field.
Heretofore the components of an extracorporeal electromagnetic flow transducer had to be maintained in a substantially rigid relationship each with the other to make certain that the device remained calibrated and functioned accurately. When all of the components were joined in such an arrangement, the device's stability was certain but the cannula of the unit was difficult to clean effectively and subject to abuse and damage from routine use and harsh cleaning procedures. Moreover, transducers of varying size had to be made to accommodate vessels and tubing of varying diameters.
Subsequently, it was found advantageous to provide a removable tubular flow contact assembly that could be easily cleaned or easily replaced, especially on clinical blood pump systems. Examples of such devices are the forceps probe illustrated herein and the embodiments disclosed in U.S. Pat. No. 4,195,515.